1. Field of the Invention
The present invention relates to a process for the production of sulfonium compounds and more particularly to a process for producing acylated sulfonium compounds by acylating the phenolic hydroxyl group of p-dialkylsulfoniophenols having a specified structure, in the presence of specified secondary amines. The term "acyl" as used herein refers to a group as derived by removal of a hydroxyl group from a carboxylic acid or a carbonic acid monoester.
2. Description of the Related Arts
Sulfonium compounds represented by the general formula: ##STR4## (wherein all the symbols are as defined hereinafter) are useful compounds for reagents for introduction of an acyl group as a protecting group in the organic chemical field, e.g., synthesis of peptides, because they exhibit acylating action in an aqueous solution.
For production of the sulfonium compounds represented by the above general formula, by acylating the phenolic hydroxyl group of p-dialkylsulfoniophenols, a method of reacting acid halides, i.e., carbonylhalogenide compounds in the presence of a base, has been generally employed. For example, Bull. Chem. Soc. Japan, 60 (7), 2409 to 2418 (1987) and Japanese Patent Application Laid-Open No. 8365/1988 disclose a method in which acid chloride is used as the acid halide, and a tertiary amine, e.g., triethylamine, as the base. In this method, not primary or secondary amines but tertiary amines are used as the base to prevent side reactions.
This method, however, is not necessarily satisfactory for practical use, because if in the acylation of the phenolic hydroxyl group of p-dialkylsulfoniophenols, the carbonylhalogenide compound and the above phenol compound are reacted in the presence of a base, e.g., a tertiary amine such as triethylamine, the yield of the desired acylated compound (sulfonium compound of the above general formula) is low, and the amine salt and by-products are not easy to separate.
For example, when p-dimethylsulfoniophenol methylsulfate and p-methoxybenzyloxycarbonyl chloride were reacted in the presence of triethylamine as the tertiary amine, the yield of the desired product, p-methoxybenzyl p-dimethylsulfoniophenyl carbonate methylsulfate, was as low as less than 30%. When N,N-dimethylaniline was used as the tertiary amine, the desired product could not be obtained at all.
When p-dimethylsulfoniophenol methylsulfate and 9-fluorenylmethoxycarbonyl chloride were reacted in the presence of triethylamine, the yield of the desired product, 9-fluorenylmethyl p-dimethylsulfoniophenyl carbonate